The present invention relates to a process for the preparation of tertiary butyl alcohol from isobutylene or hydrocarbon mixture containing isobutylene while maintaining high purity, high yield and high productivity.
There are various methods for producing tertiary butyl alcohol by the hydration of isobutylene. For instance, there is one method which employs sulfuric acid as a catalyst. According to this method no particular device is required to enhance the contact efficiency between the reaction material and the catalyst, because the catalyst itself is uniformly dissolved in the reactants. With this method, however, if unreacted isobutylene or the hydrocarbon mixture containing the unreacted isobutylene were removed by distillation from the reaction product in which the catalyst is dissolved, the equilibrium reaction permits the tertiary butyl alcohol to be simultaneously dehydrated. Thus using this procedure it is necessary to neutralize the sulfuric acid catalyst in the reaction mixture prior to recovering and refining the tertiary butyl alcohol. This means that the catalyst cannot be re-used in the process and thus economically disadvantageous.
To cope with this disadvantage various methods have been proposed which use solid catalysts that are insoluble in the reactants and which permit the solid catalyst to be present only in the reactor. As an example it is known that acidic ion exchange resins are effective as a solid catalyst, however when such a solid catalyst is used, the reaction does not proceed efficiently unless isobutylene and water are brought into intimate contact with the solid catalyst. In particular, when the hydrocarbon mixture which serves as a source of isobutylene is reacted under an elevated pressure in the liquid phase, the reaction liquid forms two phases consisting essentially of water and those hydrocarbons insoluble in the water. This phase formation makes it quite difficult to raise the contact efficiency with respect to a solid catalyst such as an ion exchange resin. Although various attempts for enhancing the contact efficiency have been reported, a satisfactory means has yet to be found.
However, U.S. Pat. No. 4,011,272 describes that when isobutylene or a hydrocarbon mixture containing isobutylene is reacted with an aqueous solution of an aliphatic carboxylic acid in the presence of an acidic ion exchange resin under conditions such that the reaction liquid forms a homogeneous solution, the catalytic efficiency between the catalyst and the reaction liquid is increased enabling the hydration reaction rate to be substantially increased. According to the process described it is possible not only to form tertiary butyl alcohol efficienctly but also to recover and refine the tertiary butyl alcohol produced thereby maintaining high purity and high yield. The sole defect inherent in the system disclosed in U.S. Pat. No. 4,011,272, however, is the formation of undesirable tertiary butyl esters of the aliphatic carboxylic acid as a by-product in small amounts during the course of the reaction. The problem is that it is difficult to separate tertiary butyl alcohol and its tertiary butyl ester by conventional distillation. Therefore, the tertiary butyl alcohol and the tertiary butyl ester in the entire amount are separated by distillation from the carboxylic acid aqueous solution and are both hydrolyzed. It is at this point that the hydrolyzed liquid must be separated into an aqueous solution of the carboxylic acid and tertiary butyl alcohol, and this requires an increased amount of heat in the form of steam.